This application relates to turbomachinery and, in particular, to a sealing device to seal the junction between a dovetail slot and the dovetail base of a blade, bucket, or airfoil in a turbine or compressor.
In turbomachinery, such as a gas turbine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Subsequent turbine stages extract energy from the combustion gases for powering the compressor and producing useful work (e.g., rotating the rotor or field of a generator).
A turbine can follow the combustor and may include one or more rows of turbine rotor blades that extract energy from the gases for powering the compressor. The turbine can power an external drive shaft that may be used for powering an electrical generator in a typical industrial gas turbine engine application.
Since the rotor blades of the turbine are subject to the hottest temperatures of the combustion gases and rotate at high speed they are subject to considerable thermal and centrifugal stresses during operation. In order to improve their life and durability, the turbine blades are typically formed of superalloys, such as nickel-based metal, for their enhanced strength at elevated temperatures.
The turbine blades or buckets typically include hollow airfoils having cooling channels therein through which is circulated cooling air bled from the compressor during operation. The blades also include an integral platform which defines the inner boundary for the hot combustion gases, with an integral supporting dovetail being disposed therebelow. The blade dovetails are mounted in corresponding dovetail slots in the perimeter of the supporting turbine rotor disk or wheel. Axial-entry dovetails are common and extend through axial dovetail slots disposed around the perimeter of the rotor disk or wheel.
Cooling air for the cooled turbine buckets can be fed from the bottom of the turbine bucket dovetail and then passes radially into the bucket. The cooling air first passes through the gap between the bottom of the turbine bucket dovetail and the rotor dovetail groove. The fit between the bucket dovetail and the rotor dovetail groove is not completely tight, and a gap exists between the respective parts. Generally, a large gap exists between the bottom of the bucket dovetail and the bottom of the rotor wheel dovetail groove. Additionally, gaps can exists between the sidewalls of the dovetail groove and the sides of the bucket dovetail. These gaps allow cooling air to escape and result in reduced engine or turbine performance.
Various coatings, such as Aluminide, have been applied to the bucket dovetail to try and reduce the size of the gap, but the gap is too large for any coatings to be completely effective or durable. Typically, a 360 degree ring is pressed against the forward and aft sides of the dovetail faces for sealing purposes. The problem with these rings is that they cannot be easily disassembled and replaced in the field. The 360 degree rings can be disassembled only when the entire rotor is disassembled. Also, when one part of the ring fails, the whole ring must be replaced. Therefore, the 360 degree ring option, is not the most desirable solution.
Accordingly, a need exists in the art for a device that can be used to effectively seal the dovetails in a turbomachine, is easy to install, and easily and quickly replaced in the field.